1. Field of the Invention
The present invention relates to fixing structure and fixing method between a link and a pin in a crawler belt which is used in a track-type vehicle.
2. Description of the Related Art
Conventionally, as shown in FIG. 15, in a crawler belt 1 which is used for a track-type vehicle in a work machine such as a bulldozer or a tractor, a plurality of track blocks 2 to contact the ground surface are mounted to an endless link chain 3 by means of bolt fastening. Then, as shown in FIG. 2 in which a part of the link chain is being exploded, when the crawler belt is being assembled, a bushing 4 is interposed between connecting portions of opposing links 6 and 7 and end portions of the bushing 4 are inserted into bushing insertion holes 34. In this state, a pin 5 is being inserted into the bushing 4. Further, end portions of the pin 5 protruding from the bushing 4 are inserted into pin insertion holes 32 and 33 of another pair of links 6 and 7 to be connected, whereby the links 6 and 7 and the pin 5 are connected and fixed to each other so as to form a joint.
With respect to the connection and the fixation of the link and the pin, Japanese Patent Application Laid-Open No. 5-213237 and Japanese Patent Application Laid-Open No. 2000-153789, of which invention was invented by the applicant of the present application and the other inventors, suggested a holding and fixing structure and a method thereof.
According to the invention as described in Japanese Patent Application Laid-Open No. 5-213237 mentioned above, there was proposed a structure which holds a link and a pin by pressing a boss of the link in a radial direction thereby protruding at least one small lump into an annular groove which was formed in a substantially arcuate shape along and around each of end portions of the pin, by means of a punch apparatus which is arranged so as to face an outer peripheral surface of the boss of the link while being aligned in the radial direction.
According to the invention as described in Japanese Patent Application Laid-Open No. 2000-153789 mentioned above, a part of an outer fixing end surface of a pin or a link is pressed in an axial direction and the pressing portion is plastically deformed in a pressing direction, so that a protruding portion is formed in a diametrical direction. Then, the link and the pin are connected and fixed to each other by allowing the protruding portion to be formed in the link or the pin, which is an opposing member to be inserted in, and by forming the protruding portion toward an engagement space which prevents a relative movement between the pin and the link in the axial direction.
According to the last-mentioned prior art, in comparison with the holding structure between the link and the pin in the first-mentioned prior art, it is possible to achieve firmer connection between the link and the pin even when the press-fitting force of the pin into the pin-press-fitting hole in the link is reduced, and it is possible to sufficiently secure the holding force of the link with respect to the axial direction of the pin. Accordingly, excellent operation and effect can be achieved in the connection and the fixation between the link and the pin.
However, in the last-mentioned prior art, formation is performed while a surface hardness of a portion to be plastically deformed is the same as a surface hardness of a portion not to be plastically deformed. Accordingly, in order to form the protruding portion in the diametrical direction by means of the plastic deformation, a great pressing force was required. That is, as a preliminary stage for performing the press-fitting and fixing, hardening and tempering are applied to the link or the pin, whereby the surface hardness thereof is increased. When the hardening and the tempering are applied, the surface hardness of the link becomes HRC 30 to 45 (HRC: Rockwell hardness), and the surface hardness of the pin becomes HRC 53 to 63. Conventionally, with these surface hardness, the protruding portion in the diametrical direction is formed by pressing the fixing end portion of the link or the pin in the diametrical direction or in the axial direction thereby plastically deforming the pressing portion.
Accordingly, in order to form a protruding portion in the diametrical direction by means of plastic deformation, pressing force corresponding to the surface hardness was required. Further, since plastic deformation is applied to the portion in which the surface hardness is high, there was a risk that a brittle fracture is generated in the plastically deformed portion, for example, by applying a strong pressing force at a stroke so as to perform plastic deformation. On the contrary, there was a problem that a long time is required for processing, in the case that pressing force is applied little by little while preventing brittle fracture from being generated. Accordingly, a special skill has been required for achieving stable fixation between the link and the pin.